Rheostat control for a window fan



March 14, 1961 c. D. VISOS 2,975,388

RHEOSTAT CONTROL FOR A WINDOW FAN Filed May 6, 1957 2 Sheets-Sheet 1 O iJ O0 024 3 r ,um, 14 f 25 O O O E i a 0 t t J 50 H J A 18 1 20 28 1219Is 2 1' as 2 54 s j I L fi J J/VV/VTOK CVzarles D. 2721505 ddorney March14, 1961 c 505 2,975,388

RHEIOSTAT CONTROL FOR A WINDOW FAN Filed May 6, 1957 2 Sheets-Sheet 2 HiLow 58 JIVPIYTOR Charles 2 Visa United StatesPatent O RHEOSTAT CONTROLFOR A WINDOW FAN Charles D. Visos, St. Louis, Mo., assignor to Knapp-Monarch Company, a corporation of Missouri Filed May 6, 1957, Ser. No.657,094

1 Claim. (Cl. 338-116) This application relates to improvements inelectrically operated fans and more particularly to new and improvedspeed control apparatus for such fans.

Several types of speed control devices for electrically operated fansare known in the prior art. Generally, such devices comprise powerregulating means connected in circuit with the fan motor to the end thatthe speed of the fan, and hence its air handling capacity, may becontrolled in a given manner. However, many of such prior art speedcontrol devices have not proved fully satisfactory for the reasonsdescribed below.

One commonly used type of prior art speed control for an electric fantakes the form of a multi-position rotary switch which may beselectively actuated to two or more preset positions, as for example,low, medium and high, to enable the fan to operate in correspondingspeeds. Manifestly, this fixed type of control is not very flexible inproviding the variety of fan speeds which may be desired by the user.Further, such speed controls generally are relatively large andtherefore cannot elficiently be mounted in the fan in the path of aircurrents to facilitate dissipation of the heat generated therein.

Accordingly, it is a general object of this invention to provide new andimproved speed control means for electrically operated fans.

It is another object of this invention to provide speed control meansfor an electrically operated fan which is continuously variable from thelowest speed position to the highest speed position, and which thereforeis adapted to provide a substantially large number of selectible fanspeeds.

it is still another object of this invention to provide an improvedspeed control means for an electrically operated fan which ischaracterized by its compactness and which therefore may be positionedin the fan housing to enable dissipation of heat by air currents withoutdetracting from the eflicient operation or the attractiveness of thefan.

It is a further object of this invention to provide an improved speedcontrol means for an electrically operated fan in which specialprovision is made for substantially reducing the problem of arcing inthe control means.

It is a still further object of this invention to provide a new andimproved speed control means for a fan, as described above, which isfurther characterized by its relative simplicity and its economy ofconstruction and operation.

These and other objects are realized in accordance with a specificillustrative embodiment of this invention in which a continuouslyvariable speed control device is connected in series with the fan motorand source of electric power. In accordance with a feature of thisinvention, the continuously variable speed control device is reduced insize by connecting the resistance windings of a plurality of rheostatsin series between the fan motor and the power source.

Each rheostat comprises a brush placed in sliding contact with itsresistance winding, so as to be variably adjustable over the entirerange of the winding. Advantageou sl'y, two rheostat brushes aremechanically coupled to each other, as by means of a contact spring, andthe brushes are operated by a manually actuatable slide knob positionedon the fan housing. Thus, the adjustment of the slide knob to any of itsrelatively great number of positions between the high speed and lowspeed ends of the rheostats result in an equal number of variances ofthe motor and fan speed. Consequently, the invention enables the amountof air delivered by the fan to be selectively varied, as desired, to anyamount within its capacity from a slight breeze to a full power airblast.

In accordance with a feature of another illustrative embodiment of theinvention, any tendency of the speed control to arc, as may result frompoor contact or loose brushes, is substantially eliminated by means of ashunt circuit connected between the low speed ends of each rheostatresistance winding. This novel shunt circuit is eifeetive to reduce thevoltage potential for creating an arc to zero when the speed controlslide knob is at the extreme low speed position, and to a value ofrelatively few volts when the slide knob is at the extreme high speedposition. Thus, at either extreme, and therefore at all intermediatespeeds, the problem of arcing in the fan speed control of the inventionis practically non-existent.

The above and other features of novelty which charactcrizc the inventionare pointed out with particularity in the claim annexed to and forming apart of this specification. For a better understanding of thisinvention, however, its advantages and specific objects attained withits use, reference is had to the accompanying drawing and descriptivematter in which is shown and described several illustrative embodimentsof the invention.

in the drawing:

Figure l is a front elevational view of a preferred embodiment of fanassembly with parts broken away;

Figure 2 is a top plan view of the fan assembly shown in Figure 1;

Figure 3 is an enlarged cross sectional view of a multispeed controldevice embodying the invention;

Figure 4 is a plan view of the multi-speed control device rheostatassembly with parts broken away;

Figure 5 is a transverse cross sectional view of the rheostat assemblytaken substantially as shown on line 55 of Figure 4;

Figure 6 is a schematic diagram of the electrical control circuit inaccordance with one embodiment of the invention; and

Figure 7 is a schematic diagram of the electrical control circuit inaccordance with another embodiment of the invention.

Referring now to the drawing and more particularly to Figures 1 and 2,the reference character 10 indicates a fan assembly which includes amain frame 12 advantageously provided with a pair of panel members 14and i6 slidably disposed at either end of frame 12. Panel members 14 and16 are adapted to permit the fan assembly It! to be used in variouswidths of window openings, and, to this end, the panel members areprovided with horizontal elongated slots 18 adapted to cooperate withscrews 19 in frame 12 to enable the width of the fan assembly to beadjusted as desired. However, it will he understood by those skilled inthe art that the panel members may be removed for enabling the fanassembly to be used in a different manner, as, for example, a floorblower and the like.

A fan housing 20 is secured to the main frame 12 and extends outwardlytherefrom for enclosing a plurality of fan blades 22 adapted to bedriven by the shaft 23 of an electric motor 24. A large central opening26 is provided adjacent fan blades 22 within the main frame 12, andsuitable safety guards 28 are secured to housing 20 at both sides of fanblades 22. Thus, the fan blades 22 are mounted so as to propel airthrough the central opening 26 and the safety guards 28 when the fan isin operation in response to the energization of the electric motor 24.Suitable brackets 30 may be secured to the main frame 12 for mountingand supporting the electric motor and fan blade assembly.

At the upper end of housing 20 there is provided a handle 32 forenabling the fan assembly to be handled and transported as desired.Located at one side of handle 32 there is a control knob 34 whichcooperates with a suitably marked plate 36 for enabling the fan to beautomatically turned on and oil at a desired temperature. The details ofthe thermostatic control which is connected to the control knob 34 arenot shown as they are well known and do not form a part of the inventionas such.

A slidable control knob 38 is provided at the other side of handle 32for controlling the speed of the fan over a continuously variable range.Advantageously, a switch plate 40 is provided with control knob 38 andis marked for various speeds between the high and low speed markings forfacilitating adjustment of control knob 38.

The multi-speed control assembly is shown in greater detail in Figures3, 4, and 5 of the drawing. In accordance with a feature of thisinvention, the novel multispeed control assembly comprises a pair ofrheostats 42 and 44 having resistance windings 46 and 48 respectivelywound upon a common resistor core 50. Advantageously, common resistorcore 50 is formed of an insulating material and may be of cylindricalshape with an annular cross section as shown in Figure 5.

A brush 52 is positioned for sliding contact with resistance winding 46,and a brush 54 is positioned for sliding contact with resistance winding48. The two brushes 52 and 54 are mechanically and electricallyconnected by means of a contact spring 56 which serves to urge eachbrush into contacting engagement with its associated resistance winding.

Advantageously, contact spring 56 is secured to the multi-speed controlknob 38 to the end that adjustment of control knob 38 in the elongatedslot 41 provided in switch plate 40 causes a corresponding adjustment ofbrushes 5?. and 54 over their respective resistance windings. Thecontrol knob 38 is formed of an insulating material and in a preferredembodiment of the invention the control knob may be formed from plasticor hard rubber.

t is an aspect of this invention that the provision of twopotentiometers connected in series by means of contact spring 56 in lieuof a single potentiometer construction enables the multi-speed fancontrol to be manufactured in a relatively compact manner, Thus, the tworheostats may be supported in a suitable housing 58 secured to the {anhousing 20 by screws 60 and 62. The compact cons ruction of themulti-speed control enables the latter to be placed in the fan housingin the path of air currents to thereby facilitate the dissipation of theheat generated therein. It further will be appreciated that this compactconstruction enables the multi-speed control to be advantageouslypositioned as described above without detracting from the efiiciency ofoperation or the attractiveness of the fan.

In accordance with one circuit embodiment of the invention as shown inFigure 6, the high speed terminal of resistance winding 46 ofpotentiometer 42 is connected to a terminal of electric motor 24. ofelectric motor 24 is connected to one side of a power plug 64. and theother side of power plug 64 is connected to the high speed terminal ofresistance winding 48 of potentiometer 44. When the multi-speed controlknob 38 is in the low speed position, or at the extreme right end ofresistance windings 46 and 48 as shown in Figure 6, the brushes S2 and54 are positioned on their respective resistance windings such that thepotentiometcrs insert a maximum resistance in the series motor circuit.Under these conditions it will be appreciated that The other terminalthe voltage across motor 24 will be at a minium and that therefore themotor will operate at its lowest speed. As the eontrolknob 38 is movedtowards the high speed end of the potentiometers 42 and 44,correspondingly less resistance is inserted in the motor circuit by thepotentiometers 42 and 44 with the result that the speed of the motor iscorrespondingly increased.

It will be understood by those skilled in the art that poor contactbetween the brushes and the resistance windings which, for example, mayresult from loose brushes, may cause arcing to taking place between thebrushes and the resistance windings of the rheostats. The voltagepotential for creating an arc will be at its maximum when themulti-speed control knob 38 is in the extreme low speed position. Theproblem of arcing is substantially eliminated by means of the novelshunt circuit shown in Figure 7 of the drawing. The circuit of Figure 7is similar to that of Figure 6 with the exception that the open or lowspeed terminals of rheostat resistance windings 46 and 48 are connectedto each other by a shunt conductor 66. The effect of shunt conductor 66i to reduce the voltage potential for creating the arc to zero when thespeed control knob 38 is in the extreme low position, since conductor 66provides a short circuit across the brushes, and to the order ofapproximately 15 or 20 volts, with a standard volt input, when the speedcontrol knob 38 is at the extreme high speed position. Manifestly, ateither the low speed or high speed positions, and consequently at allintermediate positions, the problem of arcing is substantiallyeliminated.

Thus there has been shown and described a novel multi-speed control foran electric fan which permits the speed of operation of the fan to beadjusted in a continuously variable manner over the entire range fromextreme low to extreme high speeds. Further, this unique fan speedcontrol may be manufactured in a relatively compact and inexpensivemanner, and still further the problem of arcing due to poor contact orloose brushes has been eifectlvely resolved. It will be understood bythose skilled in the art that modifications may be made in theconstruction and arrangement of the parts in the above describedmulti-speed fan control without departing from the real spirit and scopeof the invention and that it is intended to cover by the appended claimany modified forms of structure or use of equivalents which mayreasonably be included within their scope.

I claim:

In a fan structure of the type having a housing, a motor therein, and afan driven by said motor to propel air through said housing, theimprovement of a continuously variable speed control means for saidmotor comprising first and second rheostat means, a cylindrical core ofinsulating material, said first and second rheostat means comprising apair of resistance coils wound in spaced axial alignment upon saidcylindrical core, a pair of terminals, one for each resistance coil,adapted to be connected respectively to a source of power and saidmotor, and manually operable wiper means providing an electricallyconductive path between said first and second rheostat means forselectively varying the resistance in the motor circuit to enable thespeed of operation of said motor to be controlled as desired in acontinuous manner over a predetermined range of speeds, said manuallyoperable wiper means comprising a pair of spaced brushes positioned inaxial alignment for sliding contact with their associated resistancecoils, whereby the axially aligned arrangement of said coils and saidbrushes serves to minimize the depth of said speed control means toenable the latter to be placed within the housing adjacent said fan,

References Cited in the file of this patent UNITED STATES PATENTS1,339,930 Henderson May 11, 1920 1,660,979 Thayer Feb. 28, 19282,740,029 Kueser et al. Mar. 27, 1956

